Artificial limb



March 15,' 1949. G. G. HAV'ENS, 2,464,391

ARTIFICIAL LIMB Filed May 26, 1947 nnentor 6v/erm Have/75 an QNW Patented Mar. 15, 1949 OFFICE ARTIFICIAL LIMB Glenn G. Havens, San Diego, Calif., assignor' to Consolidated Vultee Aircraft Corporation, a

corporation of Delaware Application May 26, 1947, Serial No. 750,504

Claims.

The present invention relates to improvements in artificial limbs and more particularly to an improved construction for a primary weight bearing prosthetic device.

An object of this invention is to provide an improved prosthetic device having a novel construction which renders it light in weight yet having the required strength for the purpose desired and which is adapted to absorb shock energy and endure sharp blows.

Another object of the invention lies in the provisions of a natural appearing shank prosthesis oi improved construction having'a high strength to weight ratio and which utilizes a simple column as the main supporting member covered with a fairing to lend shape to the shank.

A further object resides in providing a novel construction for a prosthetic device which permits the ready building of such devices in a variety of sizes to 'it the individual amputee.

Other objects and features of the invention will be readily apparent to those skilled in the art from the following speciiication and appended drawings illustrating certain preferred embodiments of the invention in which:

Figure l is an elevational View of an articial leg embodying the present invention, with a portion broken away to show the shank construction; and

Figure 2 is a cross-sectional view taken on the line II-II of Figure 1.

Referring now in detail to the drawings, an articial limb embodying the present invention is designated by the numeral It. The artificial limb lt, as illustrated, comprises a foot section II, a shank section I2 constructed in accordance with the invention, and a thigh section I3.

The shank I2 comprises a weight bearing member which is a tubular element or column I4 formed of a high strength plastic to be described in detail hereinafter. The column I4 is connected, at its upper end, to the knee I5, in the thigh part I3 of the leg, by suitable pivotal means I6, the latter means eiecting a knee joint or hinge. The particular construction of the knee joint I6 forms no part of the present invention; any hinge device which permits the shank I2 to freely rotate relative to the thigh I3 may be utilized. The thigh section I3 is provided with-a recess or socket Il andis adapted for use with above the knee amputations. Here also the particular construction of the thigh I3 forms no part of the present invention. It is contemplated that the invention could be applied to below the knee amputations with suitable provision being made for the connection between the shank I2 which embodies the invention and the perso-n of the wearer.

The column Iii is pivotally connected or hinged in a suitable manner, at its loWer end, as at I8, to the foot portion II whereby the foot Il is adapted to move relative to the shank I2. Again the particular construction of the foot il and of the hinge I8 forms no part of the present invention, the shank I2 is adapted to be used with a variety of foot constructions and to be rotatively connected thereto in a number of ways.

Disposed about the tubular or skeletal element I4 to give shape to the shank I2 is an enclosing element or lcosmetic covering 2l. The cosmetic covering 2I extends from adjacent the knee I5 to substantially the foot I I and has the front or shin portion 22 and the rear or calf portion 23 thereof shaped to conform generally to the contour of a leg.

The cosmetic covering 2l embodies a sandwich construction which achieves a desired stiffness while maintaining a minimum weight. 'It is to be noted particularly that the cosmetic covering 2| is not designed to bear weight, its primary purpose is to provide a natural contour to the prosthesis and it is required only to have sulicient impact strength to withstand accidental blows. The weight of the wearer will be borne by the skeletal element I4.

The fairing material for the cosmetic covering 2l is comprised of a multiplicity of slabs or layers 24 of plastic foam disposed one upon the other for substantially the length of the column I4, which column Ill passes through openings provided in the individual slabs 24. The lowermost of the slabs 2A is adapted to rest upon ledge portions 25 provided by an ankle construction 26 suitably mounted at the lower end of tubular element lf2 as by bolt 2l. The remainder of the slabs 2li, as illustrated, are laid one upon the other until the desired length of shank is attained. Each of the various slabs 24 is of a somewhat different size and configuration in order that when assembled a natural leg contour will be simulated. A suitable thermoplastic bonding adhesive or glue may be employed between the various layers 24 and between the lowermost layer and the ledge portions25 of the ankle 2S to maintain the layers 24 in the position desired.

To assist in the maintenance of the various slabs 24 in assembled relation, a skin 31'! formed of plastic is disposed about the exterior of the stack, the skin 30 being secured to the outer surface of the stack of slabs 24 by an appropriate adhesive and being cured in position. The skin has desirable impact strength and provides a hard surface which is resistant to sharp blows.

Disposed over and in surrounding relation to the skin 30 is a layer 3l of sponge rubber. The sponge rubber provides a tactual quality t0 the prosthesis and further serves to eliminate such noises as occur when the shank i2 strikes hard objects.

To provide a uniform and natural color to the prosthesis and to furnish desirable smoothness, a second skin 32 is applied to the shank l2. This second skin 32 is formed of a transparent plastic, to the interior surface of which, the surface adjacent the sponge rubber, there is applied flesh colored paint. A shank l2 is thus eiiected which is easily cleaned, which resists discoloration and which gives the translucent appearance of esh.

To bridge the gaps Sil and 35 which exist between the ankle 26 and foot il a stocking 3G formed of rubber is drawn over the foot il and shank I2. It is understood, of course, that the stocking 3B is not necessary tc the invention and need not be of a suicient length to cover the entire shank prosthesis. for esthetic purposes to cover the gaps at the point of connection of the shank l2 to the foot i l, though incidentally it serves to absorb shock of accidental blows. Any device which covers the gaps may be utilized or if desired the shoe worn may be modified to provide a bridge for these gaps.

From the above description of the construction of the shank l2 it is readily apparent as to how the length of a shank can be modiiied to lengthen or shorten it to accommodate different wearers. A tubular element or' desired length is iirst chosen and then an appropriate number of plastic foam slabs Eil is applied thereon to elect a shank having the required dimensions from ankle to knee. Having a prosthesis of the desired length, the skin is cured thereon, as will be described, and a layer oi sponge rubber applied over which is fitted the skin 32 having the appearance oi flesh.

Tile compositions ci the various plastics and plastic loam that may be utlhzed in the present invention will now be discussed.

Trie plastic foam slats 2d as used here are formed of cellular cellulose acetate (which is cellulose acetate in an unoriented multicellular form). Cellulose acetate, as is weil known, is a plastic made by treating cotton linters (cellulose) with acetic acid and acetic anhydride in the presence of a suitable catalyst such as sulphuric acid, zinc chloride, o-r phosphoric acid. This plastic is aerated to effect the unoriented multiceliular form. Cellular cellulose acetate is readily workable and can be easily machined into desired shapes by the use of standard woodworking equipment. Thus the various slabs 2d mounted on the skeletal element i4 'can be readily formed into shapes which when assembled simulate the human shank. 'Cellular cellulose acetate is adapted to be bonded to itself or to skins by standard glues. Cellular cellulose acetate has a high shear strength and a relatively high impact strength in View of its low density and is well adapted for use as a iairing in the fabricationl of a shank as in the present invention.

It is understood that other plastic foams may be employed in effecting slabs for buildin-g up a shank I2 according to the present invention. For example, aerated styrene or the aerated synthetic rubbers such as butadiene acrylonitrile copoly- It is provided primarily mers are adapted for use in the construction of a shank for they possess satisfactory impact strength and have the required low density.

he transparent enclosing skin 32 disposed over the sponge rubber layer is preferably a vinyl resin plastic such as vinyl chloride-vinyl acetate copolymer resin which is provided as a transparent film. Theinterior surface' ofV this' transparent hlm is covered withilesh colored paint as required by its use in this invention. It is contemplated that other transparent plastics such as cellulose acetate, cellulose nitrate, polystyrene or ethyl cellulose in film form could be utilized in the fabrication of the shank of the present invention.

Both the inner plastic skin 30 covering the slabs 2d and the column it are preferably formed of low pressure plastic laminates which laminates are comprised of an appropriate filler impregnated with a thermosetting resin. Two principal types of thermosetting resins are adapted forlow pressure laminates. polyesters and certain of the phenolics.

The unsaturated esters arethe reaction"prod-V ucts of saturatedand unsaturated `polybasic acids (such as maleic acid, succinic acid;v phathalic` acid, citric acid, malic acid, fumaric'acid) andy saturated and unsaturated polyhydric alcohols' (such as glycerol; polyglycerols; glycols such as ethylene glycol, butyleiie glycol or trimethylene glycol; polyglycols; pentaerythritol; sorbitol'and mannitol). t is understood that the acids andV alcohols herein named aremerely representative of the polybasic and polyhydric alcohols` that may be used. As initially prepared, the un'- saturated polyesters containU a number' of unsaturated ethylenic groups which upon polymerization form cross-linked, three-dimensional structures. The unsaturated'polyesters' are 'applied as low molecular weight viscousproducts' which may be converted` through polymerization to a solid form by the application ofheat or a catalyst or by a combination of both. These resins are anhydrous, i. e., containing no Water and producing none; and because no potentially volatile material is 'split off in the form of a byproduct during the cure the" unsaturated polyester resins may be processed at low pressures'.

The phenolic resins that can be utilizd'in the present invention are those which are the reaction products of a phenolic' compound such' as phenol, creosol, Xylenol, and res'orcinol, with an aldehyde such as formaldehyde or furfural in' the presence of a suitable alkaline catalyst'(wh`ich may be ammonia, caustic alkali, or such amines as methylamine, aniline, and benzylamin'e), with the reaction taking place at a moderatey'temperature or about F. Since a thermosetting resin is required the molecular ratio of. the" phenolic to the aldehyde must be less 'than 1 to l. As is well known when the ratio is greater than'l to l a thermoplastic resin is obtained.

It has been found that phenolic resins of the type described when modified with a thermoc component such as a synthetic linear condensation superpclyamide are particularly well adapted for in low pressure laminating.

As has been stated, a low pressure plastic laminate in addition to a thermosetting resin comprises, as a'ccmponent, a ller. The functions of a filler are several; it acts as acarrier for the resins which are in a liquid or semi-monomeric state; it improves the physical characteristics of the unsupported-resin',frparticularly with respect to flexural, impact and compressive' These are the unsaturatedl strength; and it imparts design and decorative effect for specific applications.

Where high strength to weight ratios are required, as in the present invention, such fillers as fibrous glass (in woven cloth or mat form), synthetic polyamides, regenerated cellulose having a highly oriented molecular structure, linen, and high strength viscose rayon yarn may be used. Of these fillers it has been found that the fibrous glass type fillers are the most satisfactory for the particular use required by this invention because they produce laminates of exceptionally high strength with excellent impact resistance. Further, the filler is ame proof and is not affected by water or fungi. The fibrous glass is preferably provided in the form of continuous filament allglass cloths and warps or as uni-directional cloths, i. e., cloths with a glass warp and cotton flll. Before impregnation with a resin the lubricant which was added in the manufacturing process to the fibers to facilitate weaving is removed by heat treating, that is-if it has not already been pretreated by the manufacturer, to obtain maximum adhesion of the resin to the glass.

To effect a lamina the fillers and thermosetting resins arev combined in any well known manner as by brushing or as by running the filler in sheet form through a dip tank led with the desired impregnating resin and then passing the wet sheet through squeeze rollers to remove the excess resin. The impregnated filler is then molded into the desired shape by the use of any well known molding methods such as the steam infiated rubber bag method, the autoclave blanket method wherein a vacuum and steam heat is utilized, or by spirally wrapping cellophane about a sheet disposed on a mandrel and relying on the shrinkage of the cellophane during the heat cure to supply the desired forming pressure.

The following example will serve to illustrate the various steps taken in effecting laminates desirable for use in constructing the tubular element I4 and the protective skin 30 covering the plastic foam slabs 24.

An impregnating bath solution comprising a modified phenolic resin is rst prepared. This particular resinous compound comprises as one ingredient, an alcohol soluble phenol-formaldehyde condensation product condensed in the molecular ratio of from l mol phenol to 1 to 2 mols formaldehyde basically catalyzed and neutralized in a manner well known in the art, and as a second ingredient a thermoplastic modifier which is a condensation product of a carboxylic acid (havi ing the general formula COOH(CH2)7LCOOH) and a methyl diamine (of the general formula NH2(CII2)1LNH2) or urea or thiourea, with the specific condensate product utilized in this invention being formed from adipic acid and hexamethylene diamine.

These two ingredients, the phenolic resin and the condensate product of adipic acid and hexamethylene diamine are combined in a common solvent, a monohydric alcohol, with the phenolic condensate being in the proportion of 3 parts thereof to 1 part of the adipic acid-hexamethylene diamine condensate, and with the solid contents of the condensates to the alcohol being adapted to vary from 2O to 40% solids.

In the present example the bath is comprised of 64% ethyl alcohol and 36% of the resinous solids.

The filler used in this embodiment of the invention is a loi-,directional all-glass cloth treated to remove weave lubricant. This particular cloth is used because it provides desirable strength in both crosswise and lengthwise directions. The glass cloth is passed through the impregnating bath and then threaded between rubber rolls to squeeze out the excessive resinous compound taken on by the glass fabric. This immersion of the fabric in lthe solution occurs at room temperature. The impregnated fabric is then stored at room temperature to permit the ethyl alcohol to evaporate or the drying process could be accelerated by placing the fabric in an environment of elevated temperature. With the evaporation of the alcohol the weight ratio between the solid resin compound and the fibrous glass fabric will be about 27% of the solid resin to about '73% of the glass fibers. The thickness lof the impregnated fabric will be about .012 inch.

The impregnated sheet is then formed into a column by the use of a suitable tube rolling machine wherein the sheet is wrapped about a roller. A sufcient length of sheet is provided to effect a tubular element having a wall thickness of 0.125 inch which was found to be satisfactory for the present invention. The edge of the final lap is moistened with alcohol to prevent the layers loosening after removal from the machine. Curing pressure is applied to the tube by spirally wrapping a 11/2 inch strip of cellophane therearound, the cellophane shrinking during lthe heat cure. The heat cure involves placing the wrapped tube in an oven at a temperature of 330 F. for a period of about 30 minutes.

The ratio of the solid resin to the fibrous glass in an impregnated sheet can be varied over a substantial range and a satisfactory laminate still be obtained. It has been found that the solid resin content may range between 20 and 35% and the brous glass between and 65%. In the preferred embodiment detailed about 27% of solid resin was used.

The curing pressures employed in carrying out the invention may vary from 2 p. s. i. to 80 p. s. i.; at 2 p. s. i. contact is assured; at pressures above 80 p. s. i. there will be a tendency to create conditions `of resinous fluidity that may cause the resin to distribute itself unevenly throughout the laminate.

The curing temperatures may range from 280 to 350 li. The `curing time varies `according :to the thickness of the fabric and the curing pressure employed. The curing time of an impregnated fabric increases in proportion to its thickness due to the low conductivity of the impregnating materials which prevents quick uniform heating throughout the mass of the material.

A laminated tube or shaft ill built in accordance with the process above outlined and having the composition set out will have a high strength to weight ratio and will possesss high columnar strength.

A skin 30 is applied to a stack of cellular cellulose acetate slabs 24 by brushing a suitable glue upon a side of an impregnated sheet, forming the. sheet about the assembled stack, and curing in an autoclave, air being exhausted to a vacuum pressure of l5 p. s. i. and a temperature of 330 F. being supplied for ab out 10 minutes.

After the skin 3b has been applied to the slabs 2f! the sponge rubber layer 3l is fitted thereto using a suitable glue to effect adherence. A transparent vinyl film 32 having its interior surn face painted as described is then adhered to the sponge rubber layer 3l utilizing a suitable aaasci glue.,` Upon application `of this finalk skin the-` cosmetic Ycovering4 2i `is completed. Itis noted that .the vcosmetic covering 2l' may be `constructed either 'on thetubil'lar element Hl or upon asuitable. mandrel. In the present example the cosmetic coveringV 2 l is built :up utilizing a :manfdrel. When the cosmetic .covering 2l has been completed .the mandrel is removed the covering lis slipped over the tubular element l!- andthe ankles.construction` 2t mounted to Ythe tube to holdthe covering in place. The tubular element ill :is i adapted .to be secured, to attachmentyfittings located ;at.the knee l5 and foot ii to complete the assembly.

This invention exemplifies a shank vprosthesis having high `strength and low weight and which is adapted to be constructed at minimum cost. The provisionxofa single Weight bearingelement as arcorefor skeleton upon .vvhicha light. -Weight shape fde'termining, fairing is disposed, eiects a type -of construction Whichpermits of the ready making of any particular size. of artificial limb to meet-thezdemandsof theindividual amputee.

The rmaterials comprising. the skeletal element andy the -fcosmetic rcovering supported thereon have been selected because of their providing the required strength. while still being light in Weight.

It isreadily'apparent'that the construction described .fo-r the `shank prosthesis l2 is as Well adapted 1f or the making.: of other primary l Weight bearing prosthetic devices such as a forearm.`

Here the principal components would be a simple column acting es `the main supporting member which would be coveredby a fairing of plastic foam shaped to conform-to the co-niiguration of a human forearm.

Whilecertain preferred embodiments of the invention have been specifically disclosed, it is understood thatV the invention is not limited thereto, as many variations will be readily apparent tor-those skilled in the art and the invention isltorbeigiven its broadest possible interpretation Within. the terms `of thegfollowing claims.

I claim:

1. A Weight bearing prosthetic device comprising an.: elongated. columnar element adapted to bear Weight and a cosmetic covering sup-ported thereon',` said 4cosmetic covering being shaped to conform` to a human limb and comprising a plurality of layers of light weight plastic foam disposed upon fs-aid columnar. element for substantia-ilyy entire length thereof.

2. A Weight bearing, prosthetic device comprising an; elongated `columnar element adapted to bear'weight anda-cosmetic covering supported thereon, said cosmeticV covering being shaped to conform to a human limb and comprising a plurality of layers of light weight plastic foam disposed upon said columnar element for substantially the entire length thereof and a protective covering disposed on said assembled layers of plastic foam.

3. A weight bearing prosthetic device comprising an elongated element adapted to be-ar the Weight of the wearer and a cosmetic covering supported thereon, said cosmetic covering comprising a plurality of individually shaped layers of light-Weight plastic foam disposed upon said columnar element for substantially the entire length thereof, said individually shaped layers Wheninassembled relation on said columnar element providing a contour which conforms to a human limb.

4. Aweight bearing prosthetic-device compris- 8, ing'an elongated;` element adapted1to bear` the Weight of the wearerv and a cosmetic covering sup- .ported thereon; said'V cosmetici, covering being shapeduto, conform to a` human limbpand .com

prising `a plurality-Y of; individually shaped layersof. lightweight -.plastic foam .disposedtupon said.

columnar element for Isubstantially the entire length thereofiand a protective covering disposed on Vsaid :assembledflayers of plastic` foam,y said f protective covering including .a hard skin', a'layer of `rubber.thereover and ailexible `transparent skin the .interior surface of Whichis coated with flesh appearing` paint.v

5. `A Weight bearing Vprosthetic device comprising anelongated4 tubular element, formed ofL laminatedplastic, adaptedzto bear' Weight and a cosmetic covering. support-'ed thereon,

f hard skin and an outer, flexible skin coated with flesh` appearing paint.`

6.1A Weight bearingiprosthetic device comprising elongated `cylinder formed of plastic material, one end of which is pivotally afliXed at the knee of awearer and the other of which is pivotally connectedto an articial foot, and a cosmetic coveringsupp-orted thereon, said cosmetic coveringn comprising a-plurality of 'layers of plasticfoam: mountedl on said elongated cylinder and eaclrfindividually shapedwherebywhen in .resembled lrelation on said elongated cylinder the contour ofthe assembly conforms'toa human shank.

7." A Weight bearing prostheic device comprising an elongated :cylinder formed of plastic material, one end of which is pivotally. aiiixed at the knee of a wearer and the other of which is pivotally connected to an artificial foot, anda cosmeticrcoverihg supported thereon, said cosmetic covering comprising a plurality of layers of plasticfoam mounted'on'said elongated cylinder and each individually shaped vv'herebywhen in assembled relation on said elongated cylinder the contour ofthe assembly conforms to ahuman shank,` andV means applied to said fairing4 to provide' a protective coveringfor the absorption of shock energy.

8. Anarticial leg-jointed at theknee and the foot and including a shan-k portion extending from knee to foot, saidshank portion comprising a central tubular'member of a length adapted to ght of the wearer and being formed of l, vstrength plastic material, anda cosmetic coveringsimulating a Vhuman shan-k supported on l said tubular member', said cosmetic covering comprising a plurality .of layers of plastic in` cellular formation Adisposed upon said tubular member for substantially the length thereof.

9., Arr artificial leg jointed at the v.knee and the footiand including a shank portion extending fromfknee yto foot, said shanky portion comprising a central tubular; member of alength adapted toY thek height-'of the wearer and being formed of a high strength f plastic -materia1, `and `a cosmetic covering simulating a human shank supported on said tubular. member, saidv cosmetic covering comprising a plurality of layers of plastic in cellular formationl disposed upon said'tubular member Vforwsubstantially' 'the length thereof,-` and' a said' cosmetic covering being shaped to conform to a',` human limbnand comprising aplurality of layersprotective covering disposed on said assembled layers for the absorption of shock energy.

10. An artificial leg jointed at the knee and the foot and including a shank portion extending from knee to foot, said shank portion comprising a central tubular member of a length adapted to the height of the wearer and being formed of a laminated material comprising layers of a high strength filler impregnated with a synthetic thermosetting resin, and a cosmetic covering simulating a human shank supported on said tubular member, said cosmetic covering comprising a plurality of layers of plastic in cellular formation disposed upon said tubular member for substantially the length thereof, and a protective covering disposed on said assembled layers for the absorption of shock energy.

11. An artificial leg jointed at the knee and the foot and including a shank portion extending from knee to foot, said shank portion comprising a central tubular member of a length adapted to the height of the wearer and being formed of a laminated material comprising layers of brous glass fabric impregnated with a synthetic thermosetting resin, and a cosmetic covering simulating a human shank supported on said tubular member, said cosmetic covering comprising a plurality of layers of plastic in cellular formation disposed upon said tubular member for substantially the length thereof, and a protective covering disposed on said assembled layers for the absorption of shock energy.

12. An artificial leg jointed at the knee and the foot and including a shank portion extending from knee to foot, said shank portion comprising a central tubular member of a length adapted to the height of the wearer and being formed of a laminated material comprising layers of fibrous glass fabric impregnated with a synthetic thermosetting resin, and a cosmetic covering simulating a human shank supported on said tubular member, said cosmetic covering comprising a plurality of layers of cellular cellulose acetate disposed upon said tubular member for substantially the length thereof, and a protective covering disposed on said assembled layers for the absorption of shock energy.

13. An artificial leg composed of a thigh, a foot, and a shank portion interconnecting said thigh and said foot, with said shank portion comprising an elongated tubular element formed of a laminated material comprising layers of a iibrous glass fabric impregnated with a synthetic thermosetting resin and a cosmetic covering supported u by said tubular element, said cosmetic covering comprising a plurality of individually shaped layers of cellular cellulose acetate which when assembled on said tubular element provide a contour simulating a human shank, and a protective coating disposed upon said assembled layers, said protective coating comprising a hard skin adhered to the exterior surface of said layers, formed of a fibrous glass fabric impregnated with a thermosetting resin, and a exible coating arranged over said hard skin.

14. An artificial leg composed of a thigh, a foot, and a shank portion interconnecting said thigh and said foot, with said shank portion comprising an elongated tubular element formed of a laminated material comprising layers of a fibrous glass fabric impregnated with a synthetic thermosetting resin and a cosmetic covering supported by said tubular element, said cosmetic covering comprising a plurality of individually shaped layers of cellular cellulose acetate which when assembled on said tubular element provide a contour simulating a human shank, and a protective coating disposed upon said assembled layers, said protective coating comprising a hard skin adhered to the exterior surface of said layers, formed of a brous glass fabric impregnated with a thermosetting resin, and a flexible transparent vinyl resin film arranged over said hard skin.

15. An artificial leg composed of a thigh, a foot, and a shank portion pivotally interconnected with said thigh and said foot, with said shank portion comprising an elongated tubular element formed of a laminated material comprising layers of a fibrous glass fabric impregnated with a synthetic thermosetting resin and a cosmetic covering supported by said tubular element, said cosmetic covering comprising a plurality of individually shaped layers of cellular cellulose acetate which when assembled on said tubular element provide a contour simulating a human shank, and a protective coating disposed upon said assembled layers, said protective coating comprising a hard skin adhered to the exterior surface of said layers, formed of a fibrous glass fabric impregnated with a thermosetting resin, a layer of sponge rubber and a flexible transparent vinyl resin film over said hard skin.

GLENN G. HAVENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 43,031 Kirschmann June 7, 1864 2,103,511 Brown Dec. 28, 1937 2,427,457 Huck Sept. 16, 1947 FOREIGN PATENTS Number Country Date 145,764 Germany March 1903 

